FIG. 1 illustrates reflection in an optical fiber system according to prior art. A light beam 150 propagating through optical fiber 105 may create the following reflections: a reflection 91 from a proximal fiber end 129, having an intensity p1, a reflection 92A (with intensity p2′) from a distal end 121 of fiber 105 that propagates backwards through fiber 105 and emerges at proximal end 121 as reflection 92 having an intensity p2, and a reflection 93A from an environment 90 of the fiber's distal end 121, that re-enters fiber 105 through distal end 121, and propagates through fiber 105 to exit as reflection 93 with intensity p3. Overall reflection 160 at proximal end 129 may comprise reflections from proximal end 129, distal end 121 and environment 90 (91, 92 and 93 respectively). Overall reflection 161 from distal end 121 of fiber 105 comprises reflection 92A from distal end 121 itself and re-entering reflection 93 from environment 90 of distal end 121.
This theoretical separation of reflection components is very difficult to turn into a real optical separation in practice as reflected light from all sources is measured simultaneously as reflection 160.